Raphidocystis Penard, 1904 emend. Zlatogursky, 2018
Diagnosis: Centrohelids with monolayered plate-scales covering the cell surface. Plate-scales with a hollow inflected margin. Sometimes, trumpet-shaped or tubular spine-scales are present, forming an outer layer of coverings. At some life-cycle stages the siliceous scales are completely overwritten with organic spicules with some intermediate stages having a combination of siliceous spicules and scales.
References: Penard 1904, Nicholls and Dürrschmidt 1985, Mikrjukov 1996b, Zlatogursky 2018.
Type species: Raphidocystis lemani (Penard, 1891) Penard, 1904.
Arcella marginata
Arcella marginata, after Deflandre, 1929 Arcella marginata Daday, 1905 Diagnosis: Shell roughly hemispherical, rather overhanging, with a flattened, smooth edge. In dorsal view showing a